The present invention relates to an arrangement for producing plasma in a vacuum chamber with the aid of electromagnetic alternating fields, with at least one rod-shaped conductor projecting into a vacuum chamber within a tube of insulating material and the inner diameter of the insulating tube being greater than the diameter of the conductor, with at least one end of the insulating tube being held in a wall of the vacuum chamber and the outer surface of the insulating tube being sealed with respect to the vacuum chamber and at least one end of the conductor being connected to a source for producing electromagnetic alternating fields.
A known arrangement for producing plasma (DE 19,503,205) enables plasma to be produced, in a limited operating range (processing range, gas pressure, microwave capacity), as a surface treatment and coating technique. The known arrangement consists, in essence, of a cylindrical glass tube installed in a vacuum processing chamber and, having located therein, a metallic conductive tube, with atmospheric pressure prevailing in the interior space of the glass tube.
Microwave capacity is introduced at both sides through the walls of the vacuum process chamber by means of two infeeds and two metallic coaxial lines, consisting of an inner line and an outer line. Within the vacuum processing chamber, the absent outer line of the coaxial line is replaced by means of a plasma discharge, which, with sufficient conditions for ignition (gas pressure), the microwave capacity ignites and maintains, with microwave capacity being able to escape from the two metallic coaxial lines and through the glass tube into the vacuum processing chamber.
Plasma surrounds the outside of the cylindrical glass tube and, together with the inner line, forms a coaxial line having a very pronounced vaporization cover. With a fixed microwave capacity fed from both sides, the gas pressure of the vacuum processing chamber may be adjusted such that there is an evident and uniform burning of plasma along the device wherever, within the vacuum processing chamber, the outer line of the coaxial cable is absent.
In addition, an arrangement is known for the local production of a plasma in a treatment chamber, by means of microwave activation (DE 4,136,297), which chamber, by means of a flange which may be built into a wall, or by means of the wall itself, is divided into an outer and an inner part, with a device for producing microwaves being arranged at the outer part. The microwaves of which device are guided to the inner part by means of a microwave coupling device, with the microwave coupling device featuring an outer control hollow conduit, of an insulating material, which passes through the flange. Inside the outer control hollow conduit is a metal inner conduit, with microwaves from the microwave producing device being coupled in the inner conduit.
Finally, an arrangement for producing plasma in a vacuum chamber with the aid of electromagnetic alternating fields has been proposed (DE 19,722,272.2), for which a rod-shaped conductor is guided through a vacuum chamber within a tube of an insulating material and the inner diameter of the insulating tube is greater than the diameter of the conductor, with both ends of the insulating tube being held in walls of the vacuum chamber. The outer surface of the insulating tube is sealed with respect to the walls and both ends of the conductor are connected, in each case, to a first source for producing electromagnetic alternating fields. The rod-shaped conductor is surrounded, in each case, in the regions of both wall leadthroughs, in the direction of its more centered section, by a tubular piece of an electrically conductive material, with there being an amount of clearance, with the two tubular pieces being arranged concentrically to the insulating tube. In each case, the circular cylindrical intermediate spaces formed by the insulating tube and respective tubular piece are connected to a second source for producing an electromagnetic alternating field.
An object of the present invention is to create an arrangement of the type described above, which is suitable for avoiding fluctuation in the deposited coating which has its basis in the emergence of threshold fields in the microwaves.
A further object of the present invention is to avoid the the installation of costly disposable lines in order to protect the microwave transmitters from reflective capacity.
A further object of the present invention is to form antennas such that they possess, in addition to the inherent radiation characteristics of each antenna, the additional property of being able to emit high-frequency waves, without again picking up the reflected capacity as a result of using the apparatus (e.g., from the plasma).